Where there is an induced flow of liquid through equipment, such as for example domestic swimming pools, it is desirable that a uniform flow of liquid pass through the equipment at a controlled rate. With different pumping apparatus, that is not always easy to obtain and it is an object of the present invention to provide a valve which provides a relief flow therethrough which will vary automatically to allow constant predetermined uniform flow through apparatus.
Further in water filter apparatus like swimming pool cleaners, the water is drawn from a weir in the swimming pool and pumped through a sand based filter. The water then flows back into the swimming pool.
When the filter becomes dirty the resistance of the filter to water flow therethrough is increased.
When the pump is switched off the water in movement through the system has a certain inertia which causes the water flow in the system to reduce to zero only after a certain lapse of time. If the filter in the system is dirty the inertia of the water causes the pressure in the system to increase momentarily after switch off of the pump. This can have the effect of a reverse flow and cause fittings in the filter system to be released. Where the filter unit is connected to a pool cleaner this release can often render the cleaner inoperative.
The object of this invention is to provide a relief valve for the kind of application above referred to and a further object is to provide a relief valve which will also permit relief flow when necessary.